Ma'anar ƙamus na kalmar "microbe" ƙananan ƙwayoyin cuta ne, musamman ƙwayoyin cuta da ke haifar da cututtuka ko fermentation. Kwayoyin cuta ƙanana ne masu rai, irin su ƙwayoyin cuta, ƙwayoyin cuta, fungi, da protozoa, waɗanda ba su da yawa don ganin su da ido tsirara. Suna taka muhimmiyar rawa a fannoni da yawa na rayuwa, ciki har da lafiyar ɗan adam, muhalli, da samar da abinci. Wasu ƙananan ƙwayoyin cuta na iya zama masu cutarwa kuma suna haifar da cututtuka, yayin da wasu suna da amfani kuma suna da mahimmanci ga lafiyar ɗan adam da walwala.